A valve timing controller has a housing rotating with a crankshaft and a vane rotor rotating with a camshaft. The housing defines a hydraulic chamber therein. The vane rotor has a vane which divides the hydraulic chamber in a rotational direction. A rotational phase of the vane rotor relative to the housing is varied by introducing hydraulic fluid into the hydraulic chamber. JP-2004-108370A, which is a counterpart of U.S. Pat. No. 6,814,038B2, shows a valve timing controller having a spool valve which controls hydraulic fluid flow.
Specifically, in the valve timing controller, when the hydraulic fluid is discharged from a cylindrical portion, a lock pin is engaged with a recess to lock a vane rotor relative to a housing. When the hydraulic fluid is introduced into the cylindrical portion, the lock pin is disengaged from the recess to release the lock of the vane rotor. Further, the valve timing controller has a valve body provided with a plurality of ports which respectively communicate with the hydraulic chamber, the cylindrical portion, a fluid supply source, and a vent passage for discharging the hydraulic fluid. The spool valve slides in the valve body to connect and/or disconnect between the ports. When the spool valve is positioned to fluidly connect the cylindrical portion with the vent passage, the hydraulic fluid is discharged from the cylindrical portion into the vent passage, so that the vane rotor is locked. When the spool valve is positioned to fluidly connect the cylindrical portion with the fluid supply source, the lock pin is disengaged from the recess, so that the vane rotor can be rotated to vary the rotational phase thereof.
The spool valve is biased by a spring in one direction. The valve timing controller generates a driving force which moves the spool valve in the other direction against the biasing force of the spring. A lock range of the spool valve in which the vane rotor is locked is defined in such a manner as to include a stroke end of the spool valve in the biasing direction. That is, the lock range of the spool valve in which the vane rotor is locked deviates in the biasing direction from a stroke range of the spool valve in which the vane rotor can be rotated. Thus, when the hydraulic fluid supply is stopped and the driving force is not generated, the spool valve is displaced by only biasing force to lock the vane rotor, whereby an excessive vibration of the vane rotor is prevented during a successive engine start period or an engine idling period.
In the controller described above, as shown in FIG. 16, individual product variations ΔD, ΔU in driving force and biasing force applied to the spool valve are unavoidable. Thereby, relatively large variation ΔP in an axial position of the spool valve may arise, which is defined by a balance between the driving force and the biasing force, as shown in FIG. 16.
In a case that a large variation ΔP in axial position of the spool valve arises, it is necessary to set widths of the stroke range of the spool valve sufficiently large in order that the lock range where the vane rotor is locked does not overlap with the stroke range where the vane rotor is rotatable. Especially, in the valve timing controller having a configuration where the spool valve is built in the vane rotor, since it is difficult to estimate a valve characteristic, the width of the stroke range should be set sufficiently large. It may cause a long stoke of the spool valve, so that the valve timing controller becomes large in size. It is conceivable that the stroke range of the spool valve is narrowed in stead of ensuring the width of the stroke range of the spool valve. However, an adjustment width of hydraulic fluid flow rate flowing into the hydraulic chamber or the cylindrical portion becomes narrow, so that required performance can not be obtained.